1. Field of the Invention
The present invention relates to an abnormality detecting apparatus for an air temperature sensor and, more particularly, to a abnormality detecting apparatus for an air temperature sensor which is suitable for detecting an abnormality of a temperature sensor for an intake air of an engine. It should be noted that the air temperature sensor, in addition to an intake air temperature sensor of an engine, could be any air temperature sensor detecting a temperature in an engine compartment such as an air temperature sensor for an automobile air conditioner.
2. Description of the Related Art
In an electronic controlled engine, intake air temperature of an engine is used as one of the parameters which controls the amount of fuel injection. Accordingly, if the detected value of the intake air temperature sensor is inaccurate, the amount of fuel injected is not appropriately controlled. As a result, proper operation of the engine may not be maintained. In order to prevent occurrence of such a condition, it is required to detect occurrence of an abnormality of the intake air sensor with high reliability. As an abnormality detecting method for such, conventionally, a method disclosed in Japanese Patent publication 3-56417 is known. The above-mentioned abnormality detecting method for an air temperature sensor detects an abnormality of the intake temperature sensor based on the detected value of the intake temperature sensor when the engine is completely warmed up.
Generally, in a condition where the engine is completely warmed up, the temperature in the engine compartment is increased, and the intake air temperature of the engine is also increased. Accordingly, if the detected value of the intake air temperature is not increased in the state where the engine is completely warmed up, it can be regarded that an abnormality exists in the intake air temperature sensor. Thus, in the above-mentioned conventional abnormality detecting method, it is determined that the intake air temperature sensor is abnormal if the detected value of the intake air temperature sensor does not exceed a predetermined temperature in the state where the engine is completely warmed up.
When the vehicle is moving, air in the engine compartment is cooled due to air flow entering the engine compartment. Thus, if the vehicle is subjected to against wind when the vehicle is moving, the temperature increase due to radiation of heat from the engine is canceled, and thereby an increase in the intake air temperature of the engine is suppressed. In this case, even when the intake air temperature sensor is normal, the amount of increase in the detected value of the sensor is suppressed by at least a minimal amount.
On the other hand, in the above-mentioned abnormality detecting method for an intake air temperature sensor, a determination of whether or not the vehicle is in a stopped state is not performed. Thus, according to the above-mentioned abnormality detecting method for an intake air temperature sensor, when the determination of an occurrence of an abnormality of the intake air temperature is performed during movement of the vehicle, the detected value of the sensor does not exceed the predetermined value due to the influence of the wind flow due to movement of the vehicle and the against wind even when the engine is in a completely warmed condition. As a result, it is possible that an erroneous determination is made that the intake air temperature sensor is abnormal. In this respect, the above-mentioned abnormality detecting method of the intake air temperature sensor is not always a reliable method.